The present invention relates to well bore operations, and more particularly, to contained micro-particles, and methods for using such contained micro-particles in cementing operations.
Well bore fluids may be used in a subterranean formation in a number of ways. For example, hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casings and liners, are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations, such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Set cement, and particularly the set cement forming the cement sheath in the annulus of high temperature wells (e.g., those where temperatures in the well bore exceed about 230° F.), often fails due to shear and compressional stresses exerted thereon. Generally, the failure is in the form of radial or circumferential cracking of the cement as well as the breakdown of the bond between the cement and the pipe or between the cement and the formation. These failures of the cement sheath are undesirable. To counteract this problem, silica is typically included in the cement composition wherein the silica comprises fine silica flour, silica flour, micro-silica, silica sand, or mixtures thereof. However, the addition of silica to a cement composition may cause handling problems. One method to ease the use of silica in cement compositions comprises using water-silica suspensions to allow for the convenient transfer of silica into a cement composition. However, this method can be problematic because the water-silica suspensions may settle and separate over time. As a result, agitating equipment may be needed during storage of the suspensions to prevent such settling and the formation of hard cake in the bottoms of containers. Moreover, other micro-particles that may be added to a cement composition, such as fine particle-size cement, ultra-fine particle-size cement, fly ash, slag, zeolite, or vitrified shale, may present similar handling problems.